Method of forming photographic images by physical developing



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States 7 2,764,484 Patented Sept. 25, 1956 METHOD OF FORMING PHOTOGRAPHIC IMAGES BY PHYSICAL DEVELOPING N Drawing. Application September 24, 1951, Serial No. 248,102

Claims priority, application Netherlands October 3, 1950 7 Claims. (Cl. 95-88) The invention relates to methods of forming photographic images With the use of metallic mercury separated out of a mercury salt.

It is known that mercury forms two series of salts. These series of salts are referred to as mercurous compounds or Hg(I)-compounds and mercuric compounds or Hg(II)-compounds. The behaviour of mercury salts in a solution has been examined by A. Ogg; Zeitschrift Physische Chemie 27, 285 (1898), and by E. Abel Zeitschrift Anorganische Chemie 26, 361 (1901); it was then found that in such solutions an equilibrium establishes itself, which may be indicated by the diagram:

this equilibrium establishes itself very rapidly.

This ion equilibrium results in that, in the absence of metallic mercury, there may be obtained solutions of mercuric salts which do not contain mercurous ions, but that solutions of mercurous salts invariably contain not only the Hg2 +-ions but also Hg++-ions and metallic mercury. If the solution is saturated with metallic mercury, the ratio between the concentrations of Hg++ and Hgz++ is approximately 1:120, irrespective of the absolute values of these concentrations. This may be accounted for by the fact that here two kinds of ions with equal charges occur, i. e. Hg++ and Hgz++; this only applies to mercury.

From solutions containing a mercurous salt and/or a mercuric salt may be separated" out metallic mercury by the reduction of mercurous salts or mercuric salts in accordance with the diagram of reaction:

Metallic mercury may be formed from mercurous salts not only by reduction but also by other means, i. e. by

disproportioning it according to the reaction:

which is achieved by withdrawing from the equilibrium: (I) metallic mercury, (II) mercuric ions.

For carrying out the method II inter alia the following possibilities are given:

1. The formation of mercuric compounds of poor solubility;

2. The formation of mercuric compounds, for example, complex compounds of little dissociation;

3. The formation of mercuric organic compounds.

In all the aforesaid cases the result will consequently be that either by reduction or by the withdrawal of mercuric ions, metallic mercury is produced in the atom form, which is separated out of the solution in the form of mercury, if the solubility is exceeded. For the method according to the invention, it is otherwise not essential whether the mercury is exclusively produced by disproportioning or, in part also by reduction. However, the by-reaction can never be a source of trouble.

A photochemical system, in which use is made, of the reaction mentioned under H for the formation of mercury atoms is already known, inter alia from Dutch patent specification No. 46,296. According to the method used in this case, use is made of photographic layers comprising light-sensitive O-hydroxy-diazonium compounds and mercurous nitrate, which are decomposed in the areas struck by light, the product resulting from the decomposition by light then reacting with mercuric ions, which are withdrawn from the aforesaid equilibrium In this case mercury atoms are formed in substantially equivalent quantities, concentrating to mercury drops, which are subsequently amplified by physical development with the use of a developer comprising precious metal ions to form precious metal contrasts. For this purpose is, for example, used methyl-6-hydroxy-l-diazoniurn-2-benzenesulphonic acid 4 (Phot. 1. 90 b 34-40 (1950)).

The method mentioned in the aforesaid patent specification has a limitation in that the choice of light-sensitive substances producing the desired effect is very limited. Thus the incidental properties of such a substance are limiting and play a part in the determination of the usefulness of the photochemical system, for example with respect to light-sensitiveness, spectral sensitiveness, tenability and solubility and attempts have consequently been made to find other light-sensitive substances which migh give the desired result.

It has been known for a long time now that various molecules and ions having a disproportioning effect on mercurous ions are inter alia:

Sr: B. J. B. G. Guibourt, Ann. Chim. Phys. (2) 1,

CN: C. W. Scheele (1789); E. Abel Z. Annorg. Chem.

CNS: Hermes I. f. Prakt. Ch. 97, 467 (1866); I.

Fialkow Z. Annorg. Ch. 205 (1932), 235.

Nor: R. Lang I. f. Prakt. Ch. 68, 295 (1862); R. Abegg and H. Pick Z. Annorg. Ch.'51, 20 (1906);

$203 1 S02 or 803 M. L. Pan de St. Gilles Ann.

Chim. Phys. (3) 56, (1852); E. Divers & T. Shimidzu J. Chem. Soc. 49, 533 (1886);

NHs or NH4+z of which the reaction with calomel and sublimatehas been known for a long time and organic amino-compounds, for example also pyridine and the corresponding ammonia ions, thiourea and derivatives.

it is furthermore known that these molecules and ions react both with mercuric compounds and with mercurous compounds, the same mercuric compound being usually produced; in the latter case, however, metallic mercury is produced in addition.

It has been found possible to produce various lightdecomposition products by photochemical means, these. products being capable of eliminating the mercuric ion from mercurous compounds, for example solutions of mercurous nitrate, thus carrying out the disproportioning of the mercurous ions. Then metallic mercury is separated out and concentrated. to mercury germs, which may be amplified in a manner otherwiseknownper se to form metal images by means of physical development. been found that for this purpose either organic compounds or inorganic compounds may be used.

Light-sensitive. substances which may be used success fully, ,must meet the requirement that: V

(1) upon exposure they should separate disproportioning or reducing molecules or ions;

(2) they should be so stable in darkness that mercuric ions do not withdraw these molecules or ions from the compound during the time of reaction;

It has.

(3) they should not have a disproportioning or reducing effect on mercurous ions.

Whether a particular substance fulfils this requirement may be ascertained in a very simple manner.

For this purpose is made a solution, for example, of 0.1 m.; this is divided into two parts: one part is exposed a mercurous nitrate solution is then added to both parts. The solution not exposed must not separate out metallic mercury, whereas the solution exposed should do so. Disproportioning may be shown by potentiometric titration or by a qualitative reaction.

Thus, for example, it has been found that light-sensitive compounds containing sulphide ions, always react and are hence not suitable and that particularly in the class of sulphite compounds and cyanide compounds particularly suitable light-sensitive substances are available;

which the CN-group of the --N2CN-group becomes ionisable by exposure. Moreover, bisulphite compounds of aldehydes, for example, of nitro-benzaldehyde yield satisfactory results. 5 For the manufacture of photographic images according to the invention, a lyophile layer, for example, paper, re-generated cellulose or textile may be soaked in a solution of a light-sensitive compound. Subsequent to the exposure the layer is introduced into a solution containing mercurous ions for example 0.01 n mercurous nitrate and then into a physical developer. However, as an alternative, the mercurous nitrate may be already added to the sensitizing liquid.

Examples of substance suitable for the photochemical manufacture of the said molecules and ions reacting with mercury ions are:

Substances Mode of Preparation 4[ 0(CN)s] Gi' clinl\sI Handbuch der Anorganischcn Chcmie, 8th cditlon, system No. 53,

page 0. 199.

K4[W(ON)B] Same, system No. 54, page W. 201.

K [Mo(CN)a] Same, system No. 53, page M0. 203.

K3[ e(CN)8]- Potassium ferric cyanide (a previously analyzed preparation was used).

Na [Fe(CN)5(NO)] Sodium nitro-prusside (a previously analyzed preparation was used).

K [G0(CN)u] Inorganic Syntheses II. page 225. h

Ka[Rh(CNS)o] Gmelinghfiandbuch der Anorganischen Chemie, 8th edltwn, system page 83.

K3[CI(ONS)B1 Gmelin-Krauts Handbueh der Anorganischen Chemie, 7th edition, olu e 3,

chapter 1, page 655.

Nas[C0(N02)o] Commercially available preparation was used.

K[O0(NH:):(NO2)41 Gmclins Handbuch der Anorganischcn Ohemie, 8th edition, system page 00(3) 316.

Sa e, system Nr. 58, page 00(A) 399.

Same, system Nr. 58, page Oo(B)278.

Same, system Nr. 58, page Co (B) 302. v 2.5 g. carbonate-tetrammine-cobaltmitratc, 00(NH3)4(CO3)N03, cf. Gmelins Handbuch der Anorganischcn Ohemie, 8th edition, system Nr. 58, page 0003) 279, was intimately mixed with 0.75 g. of thionren, 1.3 g. of glacial acetic acid and 1 com. of water in a mortar, carbon dioxide gas being evolved thereby. After some time an additional small amount of acetic acid was still added, whercafter, the mixture was again rubbed in the mortar. After two days had lapsed, the pink-colored co pound was drawn ofi, washed in small portions with alcohol and then dried, thus yielding this compound.

of diaquo-dichloro-diamine-eobaltichloride, C0(NHa)2(H2O)2C1gOl, cf., Gmelins Handbuch der Anorganischen Chemie, 8th edition, system Nr. 58, page 00(13) 249, was powdered and scattered into a cooled solution of 1.5 g. of potassium-chloride, 0.7 g. of thionrea and 0.59 potassium carbonate in 5 com. of hot water (pH about 11). The liquid turned reddish-brown and a precipitation was formed which, after cooling for min. in ice, was drawn ed and washed with water and alcohol; the precipitate was dried in air, yielding a black powder. Any small quantity of unreactcd thiourea still present tn the powder, was removed by dissolving the powder in a 10% solution of acetic acid in water, followed by precipitating with the aid of mercuric-nitrate.

this also applies to the class of nitrites, ammonia and de rivatives, rhodanides and various organic compounds.

, These ions and molecules are preferably used in the form of stable complex compounds, in which the disproportioning molecules or ions are bound to at least one central metal ion, whilst, moreover, particularly the organic cyanogen compounds and sulphite compounds also exhibit the desired effect.

Use may be made of complex compounds of many metal ions, such for example as the complex compounds of Cr(III), Fe(III), Co(II I), Rh(III), Mo(IV), Mo(V), W(IV), Mn(III). Particularly the cyanogen ion forms sufficiently stable complex compounds with many metal ions, these compounds being usually decomposed upon exposure to visible light or to light on the verge of ultraviolet. Complex metal compounds are not light-sensitive on a photographic sense cannot be used for the method according to the invention, such for example as complex platinum cyanides which, upon exposure, fluoresce and do not dissociated.

As a matter of course the pH at which these complex compounds are used should be taken into account with a view to their stability. Of the organic cyanogen compounds are particularly suitable the cyanogen hydrides of aldehydes, more particularly of aromatic aldehydes. The absorption spectrum of these compounds may be rendered favourable by the introduction of substituents, particularly nitro-groups into the core. Excellent compounds are, for example, orthoand paranitro-almond acid nitril. Furthermore very good results are obtainable with the use of diazo-cyanides, in

With reference to a few examples it will now be explained how such substances may be used for the manufacture of photographic contrasts.

Example I superficially saponified cellulose-acetate foil is sensitized by immerging it for two minutes in a 0.05 molar solution of sulphitodiaethylene-diamine-cobaltichloride CO(C2H4N2H4)2SO3C1 and by drying it in air. With the use of a 500 W. mercuryvapour lamp a seusitometer key was copied on this material in one minute (AD=0.2). The copy was transiently immerged in a 0.01 11 solution of mercurous nitrate in 0.01 n nitric acid, Washed in water and developed for 4 minutes in a physical developer containing 5 gr. of metol, 20 gr. of citric acid and 4 gr. of silver nitrate in l l. of water.

On the copy six steps showed a blackening of more than 2, five steps, a blackening of between 0 and 2, whilst the remaining part was blank.

With the use of a mercury vapour lamp an image negative was printed in contrast on this material; after the aforesaid treatment the positive image showed an excellent gradation having satisfactory details in light and shadow and an excellent sharpness. The colour is 70 neutral grey to black.

Example II treated in a manner similar to that described under Example I. The images obtained have a steeper gradation and the sensitiveness is slightly smaller than with Example I.

Example III A foil similar to that mentioned above in the above examples is soaked in a saturated aqueous solution of potassium-diamino tetranitro-cobaltiate This solution is less than 0.1 molar. In the manner described above (development for five minutes) ten steps of the sensitometer key were reproduced: the blackening did not exceed 2. The gradation is soft with a satisfactory half-tone reproduction; the sharpness is satisfactory, the colour is neutral grey.

Example 1V superficially saponified ethylcellulose is soaked for 2 minutes in a 0.1 molar solution of O-nitrobenzaldehyde cyanogenhydrine in 40% alcohol, then wiped and dried. Subsequent to exposure under a negative with the use of a mercury-vapour lamp this material is bathed for a short time in a solution containing 0.01 to 0.1 mercurous nitrate; it is then physically developed in 0.5% metol-2% citric acid-0.4% silver nitrate -for 5 minutes. Very smart diapositive pictures of neutral grey to deep black in colour, having an excellent halftone reproduction and a great contrast effect is obtained.

By using chromogene physical developers, such as described, for example, in patent application U. S. application Serial No. 227,564, filed May 22, 1951, a pigment image may be produced in the area of and instead of the precious metal image. Then the precious metal image may, if necessary, be eliminated by means of one of the known attenuators, so that only a pigment image is left.

What We claim is:

1. A method of producing photographic contrasts comprising the steps, selectively exposing a light-sensitive layer containing a salt of a complex ion consisting of a metal selected from the group consisting of Co, Cr, Fe, Rh, Mo, W and Mn and at least one member of the group consisting of Cu, CNS, NO2 SO3, 8203-, NHz, C5H5N, and

R being a member of the group consisting of hydrogen and alkyl, to partly decompose said salt at selected portions of the layer, then applying to said exposed layer an aqueous solution of a water soluble mercurous salt to form latent mercury contrasts, and physically developing the mercury contrast by applying to the mercury contrast an aqueous solution of a salt of a noble metal reducible to metal and a reducing agent for said metal so as to deposit said noble metal on said mercury contrast.

2. The method of claim 1 in which the member is CN.

3. The method of claim 1 in which the member is NS 4. The method of claim 1 in which the member is SOs 5. The method of claim 1 in which the member is 5203 6. The method of claim 1 in which the member is N02.

7. The method of claim 1 in which a color photographic contrast is also formed and the reducing agent for said metal is an organic reducing agent the oxidation product of which yields an insoluble organic dye contrast simultaneously in place with a metal contrast.

References Cited in the file of this patent UNITED STATES PATENTS 345,753 West July 20, 1886 641,919 Andresen et al Jan. 23, 1900 674,227 West May 14, 1901 1,976,302 Sheppard et a1. Oct. 9, 1934 2,020,853 Pels Nov. 12, 1935 2,067,690 Alink et al. Jan. 12, 1937 2,150,834 Holst et a1. Mar. 14, 1939 2,183,447 Dippel et a1 Dec. 12, 1939 2,571,670 Bos'et a1. Oct. 16, 1951 2,571,671 Bos et a1. Oct. 16, 1951 FOREIGN PATENTS 232,307 Great Britain Apr. 9, 1925 OTHER REFERENCES Eder Ausfuhrliches Handbuch De Photographic (1929 vol. IV, part 4, 3rd. ed., pub. W. Knapp, Germany, pages 21, 26, 156, 193, 200 and 201. 

1. A METHOD OF PRODUCING PHOTOGRAPHIC CONTRASTS COMPRISING THE STEPS, SELECTIVELY EXPOSING A LIGHT-SENSITIVE LAYER CONTAINING A SALT OF A COMPLEX ION CONSISTING OF A METAL SELECTED FROM THE GROUP CONSISTING OF CO, CR, FE, RH, MO, W AND MN AND AT LEAST ONE MEMBER OF THE GROUP CONSISTING OF CN-, CNS-, NO2-, SO3--, S2O3--, NH3, C5H5N, AND 